1. Field of the Invention
The present invention relates to a fluid pressure apparatus of a fluid pressure cylinder or a fluid changeover valve or the like, and more specifically, concerns a fluid pressure apparatus in which an improved packing is installed to a partitioning member comprising a piston or a spool or the like, which moves in the interior of a slide hole defined in a housing.
2. Description of the Related Art
A fluid pressure cylinder generally includes a piston that moves in an axial direction along the interior of a slide hole formed in a housing. A packing (o-ring) made of an elastic rubber material is installed on the outer circumference of the piston, such that through the packing, sealing is effected between the inner circumference of the slide hole and the outer circumference of the piston (For example, see Japanese Laid-Open Patent Publication No. 09-072310 and Japanese Laid-Open Patent Publication No. 2003-120602).
Further, in such conventional techniques, together with the packing, a wear ring is provided on the piston, the wear ring being made from a material (e.g., a synthetic resin) having a hardness greater than that of the packing and which is superior in terms of slidability. In the case that a transverse load acts on the piston in a direction tending to cause misalignment between the axis of the slide hole and the axis of the piston (i.e., in a direction perpendicular to the piston axis), misalignment of the piston axis is suppressed by the wear ring, and excessive deformation of the packing due to pressing of the inner surface of the slide hole against the packing is prevented. Also, the outer circumference of the piston is prevented by the wear ring from coming into contact with the inner circumference of the slide hole.